Many engines have already been designed along the same lines. Thus, there are spark-ignition 4-stroke engines having 4 valves per cylinder, a plug placed in the cylinder head on the longitudinal axis of the cylinder having oriented intake ducts and ending up substantially parallel to the axis of the cylinder, where the fuel injector ends up just below the intake valves.
There are also well-known engines of this type wherein the intake lines are however oriented so as to produce a motion of the gas around the axis of the cylinder (a motion known as swirl).
The piston associated with these engines commonly exhibits a recess of specific shape intended to orient and to reinforce the motion of the gas in the combustion chamber.
Also known are engines whose piston comprises a spherical howl (or recess) placed, at the top dead center, just opposite the fuel injection and the spark plug.
All these engines have large cylinder capacities (cylinder bores above 80 mm) and they all have at least four valves per cylinder.
They allow stratified combustion at low loads and/or homogeneous combustion at high loads.
The combustion is referred to as stratified when a zone of the combustion chamber contains a richer mixture than the rest of the chamber at low loads. This allows the mixture to be more readily ignited since the enriched zone is in the vicinity of the plug.
A combustion referred to as homogeneous is recommended at high loads. A highly homogeneous mixture is thus sought throughout the combustion chamber.
Direct-injection engines currently run properly with either one mode or the other. It is generally difficult to reconcile the two methods of operation.